1. Field of the Invention
The present invention relates generally to a focal-plane shutter for a camera and, more particularly, to a focal-plane shutter having a structure effective for preventing a slit forming sector from colliding with an edge portion of a shutter opening.
2. Description of the Related Art
In a conventional focal-plane shutter for a camera, an open shutter sector group comprising a plurality of shutter sectors is provided rearward of a base plate having a shutter opening, a partition plate having a partition plate opening is arranged rearward of the open shutter sector group, a close shutter sector group comprising a plurality of shutter sectors is provided rearward of the partition plate and a sector holding plate having a holding plate opening is provided rearward of the partition plate via a sliding plate. Further, the open shutter sector group and the close shutter sector group respectively execute the operation of opening and closing the respective openings of the base plate, the partition plate and the sector holding plate by moving the respective shutter sectors by different displacement amounts by use of a plurality of arms respectively having parallel link mechanisms. (An example of such a structure is disclosed, for instance, in Japanese Patent Laid-Open No. 20534/1995). The open shutter sector group and the close shutter sector group each comprise one slit forming sector and a plurality of cover sectors.
The structure of the close shutter sector group and the partition plate is illustrated in FIG. 2. A close shutter sector group 4 comprises a single sheet of a slit forming sector 41 and three other sheets of cover sectors 42, 43 and 44. When a partition plate opening 31 of a partition plate 3 is closed by the close shutter sector group, the slit forming sector 41 is moved prior to the other cover sectors 42, 43 and 44, the other cover sectors follow the slit forming sector 41 and the respective sectors are moved by different displacement amounts to thereby execute operation of completely closing the partition plate opening 31 of the partition plate 3.
Meanwhile, when the partition plate opening 31 of the partition plate 3 is closed by the close shutter sector group 4, the respective shutter sectors 41 through 44 move from a lower end portion of the partition plate opening 31 in an upward direction, and there is a case in which a front end edge portion 41a in the moving direction of the slit forming sector 41 collides with an upper end portion (upper edge portion) 31a of the partition opening 31. Therefore, there is a case in which the upper end portion 31a of the partition opening 31 or the front end edge portion 41a of the slit forming sector 41 may be damaged. In order to prevent the collision, as shown in FIG. 2, there has been proposed a construction in which the upper edge portion 31a of the partition plate opening 31 is formed in a shape of a gradually-inclined slope. However, even with a construction in which the upper edge portion 31a of the partition plate opening 31 is formed in the shape of the gradually-inclined slope, the slit forming sector 41 may occasionally collide with the upper edge portion 31a of the partition plate opening 31.
Hence, there has been proposed a construction in which the partition plate 3 is formed to bend, for example, in a gradually-inclined inverse-slope type shape at a vicinity of a center line in a vertical direction in FIG. 2 to thereby provide a small gap between the partition plate 3 and the slit forming sector 41 of the close shutter sector group 4. However, an unavoidable problem occurs due to the leakage of light when such a gap is present.
In order to resolve the above-described problems associated with the previously-proposed structure, the present invention provides a focal-plane shutter for a camera having a projected portion for preventing sector collision, the projected portion being disposed at one of a base plate, a partition plate, and a sector holding plate, the position of the projected portion being a position into which a slit forming sector is brought into contact immediately before the slit forming sector reaches an end portion of an opening and from which the slit forming sector is separated in a state in which the shutter sector group stops closing the opening.
By the foregoing construction, collision between a front end of the slit forming sector and the end portion of the opening of the partition plate or the like can be prevented with a degree of certainty and the leakage of light through the shutter is also prevented.